Download The Cardiac Cycle

The Cardiac Cycle
The Cardiac Cycle
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The repeating pattern of contraction
(systole) and relaxation (diastole) of the
heart
Duration of cardiac cycle = 0.8 seconds
Diastole longer than systole
Ventricular contraction follows atrial
contraction (0.1 to 0.2 second later)…why?
The Cardiac Cycle
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The end diastolic volume: the total volume
of blood in the ventricles at the end of
diastole (120 ml)
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Stroke volume is the volume of blood
pumped by each ventricle per beat (70 ml)
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Residual volume: amount of blood left in
each ventricle at the end of systole (50 ml)
The Cardiac Cycle
Isovolumetric ventricular contraction
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Ventricles contract
Ventricular pressure: increasing
Ventricular volume: no change
AV valves: closed.. prevent backflow of
blood
Semilunar valves: closed (P in ventricles <
P in vessels)
Heart sounds: 1st heart sound
ECG: QRS complex
The Cardiac Cycle
Ejection phase
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Ventricular pressure: increasing > the
pressure in the aortic and pulmonary
vessels
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Left ventricular pressure up to 120 mmHg
Right ventricular pressure up to 25 mmHg
Ventricular volume: decreasing
Semilunar valves: open
AV valves: closed.. prevent backflow of
blood
The Cardiac Cycle
Isovolumetric relaxation
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Ventricles relax
Ventricular pressure: decreasing
Ventricular volume: no change
AV valves: closed
Semilunar valves: closed
Heart sounds: 2nd heart sound
ECG: T wave
The Cardiac Cycle
Rapid filling of the ventricles
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Ventricular pressure: below atrial
pressure ( slightly above zero)
Ventricular volume: increasing
AV valves: open when pressure in the
atria> the pressure in the ventricles
Semilunar valves: closed
Passive ventricular filling via AV
valves (80%)
The Cardiac Cycle
Atrial systole
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Active filling of the ventricles (20%)
Ventricular volume: slight rise
Ventricular pressure: slight rise
Semilunar valves: closed
AV valves: open
ECG: P wave
The Cardiac Cycle
1.
2.
3.
4.
5.
Isovolumetric
contraction
Ejection phase
Isovolumetric
relaxation
Rapid filling of the
ventricles
Atrial systole
Heart Sounds
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The first heart sound:
 Cause:
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closure of the AV valves
The second heart sound:
 Cause:
closure of the semilunar valves
Cardiac Output
Cardiac Output
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Cardiac output is the volume of blood
pumped by each ventricle per minute
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CO
= Stroke volume x Heart rate
(L/min) (ml/beat)
(beat/min)
= 70 X 70
= 4900 ml/min
= 5 L/min
 Normal cardiac output (CO) = 5 L/min
Cardiac Output
Cardiac Output
Regulation of Heart Rate
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Sympathetic stimulation
  HR (positive chronotropic effect)
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CO
Parasympathetic stimulation
  HR
  CO
Cardiac centers in the medulla oblangata
Cardiac Output
Regulation of Stroke Volume
End Diastolic Volume (EDV)
 Frank- Starling Law of the Heart
 venous return   EDV   length of
cardiac muscle (stretch)  force of
contraction  stroke volume 
 cardiac output
Cardiac Output
Regulation of Stroke Volume
 Positive ionotropic effect  strength of
contraction
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Sympathetic stimulation
Adrenaline
Negative ionotropic effect   strength of
contraction
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Parasympathetic stimulation
Acetylcholine
Vagal stimulation